SAN DIEGO -- The rain-swollen Tijuana River breached its banks just north of the Mexico line Wednesday, trapping people and horses by the dozens in trash-laden stormwater until emergency crews were able to rescue them.

Several people suffered exposure and three horses drowned when the waterway out of Baja California overflowed and inundated the surrounding swampy valley west of San Ysidro around noon, according to the San Diego Fire-Rescue Department.

Another horse had to be euthanized due to severe barbed-wire cuts it suffered while trying to escape the rising waters, SDFRD spokesman Maurice Luque said.

In all, lifeguards and firefighters rescued about two dozen people -- six of whom were extricated from a flooded residential property by helicopter -- and pulled roughly 40 horses from the frigid floodwaters with help from Border Patrol and Humane Society personnel.

The crews had to help ranchers deal with some spooked stallions that were kicking and biting each other in the deluge.

Medics took three men, ages 29, 33 and 45, to Scripps Mercy Hospital Chula Vista for treatment of non-life-threatening hypothermia, Luque said.

San Diego police officers closed stretches of several roads in the river valley, including Hollister Street, SDPD spokeswoman Monica Munoz said.

The Tijuana River, which flows into the United States just west of San Ysidro Port of Entry, frequently carries rubbish and sewage out of Mexico, across a floodplain in the far southern reaches of San Diego, and into the ocean near Imperial Beach.

An unusually large amount of debris in the river apparently worsened Wednesday's overflows by creating "mini-dams" that slowed the waterway's seaward currents, Luque said.

In the city of Tijuana, the river is contained in a large concrete flood channel.